Effects of cell division, cell density, and cyclic nucleotides on choline acetyltransferase activity in a cholinergic neuroblastoma cell line (S-20Y)

Effects of sex hormones, forskolin, and nicotine on choline acetyltransferase activity in human isolated placenta

The activity of choline acetyltransferase (ChAT) was investigated in the human placenta before and after long-term incubation (24 h) to test the effects of sex hormones, nicotine and forskolin. ChAT activity differed considerably between the amnion (0.03 micromol/mg protein/h) and the villus (0.56). After long-term incubation, ChAT activity persisted in the latter but declined in the amnion. Neither sex hormones (beta-estradiol, testosterone, progesterone; 10 or 100 nM each) nor follicle stimulating hormone and luteinizing hormone (FSH/LH; 8.4 U/ml each) modified ChAT activity. Also nicotine (1 nM-100 microM) did not affect ChAT activity. Forskolin, an activitor of adenylyl cyclase, reduced ChAT activity in the villus but not in amnion. The present model offers the possibility to investigate ChAT regulation in intact tissue under long-term incubation. The risks of maternal smoking during pregnancy cannot be attributed to an effect of nicotine on placental ChAT activity. Differences in the regulation of ChAT appear to exist between neuronal and nonneuronal cells.

Overexpression of a neuropeptide nociceptin/orphanin FQ precursor gene, N23K/N27K, induces neurite outgrowth in mouse NS20Y cells

We recently discovered N23K and its splicing variant N27K as transcripts upregulated in mouse NS20Y cells after differentiation induced by dibutylyl cyclic AMP (dbcAMP) treatment. N23K and N27K encode precursor proteins for an opioid neuropeptide, nociceptin/orphanin FQ, but the transient expression of N23K and N27K suggests that it may be involved in neuronal differentiation. In the present study, we report that NS20Y cells transfected with N23K and/or N27K but not with vector alone formed neurites, with the expressed protein distributed in the perinuclear region and distal parts of the neurites. The granular staining of the N23K and N27K proteins was also colocalized with secretogranin I, indicating incorporation into large dense core vesicles. This cellular targeting of the N23K and/or N27K protein is similar to that of dbcAMP-induced processes in nontransfected NS20Y cells. In addition, the neurites of transfectants that expressed both N23K and N27K were longer than those of the transfectants that expressed N23K or N27K alone. Our results demonstrate that N23K and N27K participate in the regulation of neurite outgrowth.

Histone hyperacetylating agents stimulate promoter activity of human choline acetyltransferase gene in transfection experiment

Butyrate (5 mM), Trichostatin A (1 microM) or Trapoxin A (30 nM) increased choline acetyltransferase (ChAT) activity in cultured rat sympathetic neurons 3- to 8-fold in 2 days. On the contrary, the three drugs decreased ChAT activity in human CHP126 cells. Butyrate had little effect on ChAT mRNA level in these cells, suggesting post-transcriptional mechanisms for the decrease in ChAT activity. However, transient transfection experiments using CHP126 cells revealed that the M promoter, but not the R promoter, of human ChAT gene was activated 20- to 130-fold by the three hyperacetylating agents. A butyrate-responsive element was localized in the 1 kbp region upstream of exon M. Constructs containing in addition the genomic segment between exons M and 1 displayed maximal basal activity and inducibility by butyrate, suggesting the presence of butyrate-activated promoter/enhancer elements in this region. The stimulatory effects of butyrate and Trichostatin A were also observed in stably transfected CHP126 clones, suggesting that the chromatin environment was not preventing the induction of the endogenous ChAT gene by butyrate. Rather, the data suggest different chromatin organizations for the stable transgene and the endogenous ChAT gene.

Molecular cloning and characterization of a novel form of neuropeptide gene as a developmentally regulated molecule

To examine the molecular basis controlling neuronal differentiation, subtraction library construction and differential screening were used to identify cDNAs whose mRNA levels are regulated in mouse NS20Y cells by dibutyryl cyclic AMP treatment. One of them, N27K, whose mRNA increases transiently during both neuronal differentiation in NS20Y cells and development in mouse brain. The deduced amino acid sequence of N27K comprises 212 amino acid residues and is a novel form of a precursor protein for a new neuropeptide nociceptin/orphanin FQ, which we independently cloned as N23K. That is, the putative protein encoded by N27K is 25 amino acids longer than that encoded by N23K. Using an antibody against a C-terminal peptide of the N27K protein that recognizes a 27-kDa protein in Western blot analysis, a punctate structure in the perinuclear region and areas near the tip of neurites is visualized in neurally differentiating NS20Y cells. The time of maximal expression correlates with periods of neurite extension, and expression decreases as the neuritic network develops. Immunohistochemistry of tissue sections of the mouse central nervous system revealed that reactivity for the anti-N27K protein antibody can detected in early generated neurons at embryonic day 14, in virtually all immature neurons at postnatal day 1, and in subsets of neurons of discrete brain regions such as the hypothalamus and spinal cord in adults. This remarkable redistribution suggests that N27K may be involved in a process in neurite outgrowth and nervous system development.

Cell type-specific interactions of transcription factors with a housekeeping promoter in vivo

Mammalian housekeeping promoters represent a class of regulatory elements different from those of tissues-specific genes, lacking a TATA box and associated with CG-rich DNA. We have compared the organization of the housekeeping Htf9 promoter in different cell types by genomic footprinting. The sites of in vivo occupancy clearly reflected local combinations of tissue-specific and ubiquitous binding factors. The flexibility of the Htf9 promoter in acting as the target of cell-specific combinations of factors may ensure ubiquitous expression of the Htf9-associated genes.

Transcriptional regulation of choline acetyltransferase gene by cyclic AMP

The effect of cyclic AMP on the gene expression of choline acetyltransferase (ChAT) was studied in NG108-15, mouse neuroblastoma and rat glioma hybrid cell lines. Addition of dibutyryl cyclic AMP to the culture medium increased both the ChAT mRNA level and ChAT activity twofold. Polymerase chain reaction analysis of the ChAT mRNA indicated that, among the multiple mRNA species, M-type mRNA was transcribed most efficiently, with or without the addition of dibutyryl cyclic AMP. The 5' region of the mouse ChAT gene was ligated to the bacterial chloramphenicol acetyltransferase gene, and the expression of chloramphenicol acetyltransferase activity was determined by transfection analysis. Cyclic AMP derivatives enhanced the reporter gene expression in both transiently and stably transfected cells. DNA deletion analysis indicated that the intron region downstream of the M-type exon is necessary for the cyclic AMP responsiveness, and that cyclic AMP derivatives increase ChAT gene transcription mainly from M-type promoter. These results suggest that a cis-acting DNA element that confers the cyclic AMP responsiveness of the ChAT gene is present in the intron downstream of the M-type exon.

Cyclic AMP regulation of the human choline acetyltransferase gene

Regulation of the human choline acetyltransferase gene by 8-bromo-cAMP was investigated by transfecting into NS-20Y cells choline acetyltransferase promoter sequences fused to the reporter gene firefly luciferase. Promoter activity was localized to nucleotides -163 to +73. This region of the gene responded to 8-bromo-cAMP in a similar fashion as the endogenous enzyme. However, nearly the same induction was observed for constructs containing unrelated promoters. Furthermore, fusion of the choline acetyltransferase gene to the thymidine kinase promoter yielded no increased induction by 8-bromo-cAMP. These results suggest that cAMP regulates choline acetyltransferase gene transcription through an indirect mechanism.

Acetylcholine transport, storage, and release

ACh is released from cholinergic nerve terminals under both resting and stimulated conditions. Stimulated release is mediated by exocytosis of synaptic vesicle contents. The structure and function of cholinergic vesicles are becoming known. The concentration of ACh in vesicles is about 100-fold greater than the concentration in the cytoplasm. The AChT exhibits the lowest binding specificity among known ACh-binding proteins. It is driven by efflux of protons pumped into the vesicle by the V-type ATPase. A potent pharmacology of the AChT based on the allosteric VR has been developed. It has promise for clinical applications that include in vivo evaluation of the density of cholinergic innervation in organs based on PET and SPECT. The microscopic kinetics model that has been developed and the very low transport specificity of the vesicular AChT-VR suggest that the transporter has a channel-like or multidrug resistance protein-like structure. The AChT-VR has been shown to be tightly associated with proteoglycan, which is an unexpected macromolecular relationship. Vesamicol and its analogs block evoked release of ACh from cholinergic nerve terminals after a lag period that depends on the rate of release. Recycling quanta of ACh that are sensitive to vesamicol have been identified electrophysiologically, and they constitute a functional correlate of the biochemically identified VP2 synaptic vesicles. The concept of transmitter mobilization, including the observation that the most recently synthesized ACh is the first to be released, has been greatly clarified because of the availability of vesamicol. Differences among different cholinergic nerve terminal types in the sensitivity to vesamicol, the relative amounts of readily and less releasable ACh, and other aspects of the intracellular metabolism of ACh probably are more apparent than real. They easily could arise from differences in the relative rates of competing or sequential steps in the complicated intraterminal metabolism of ACh rather than from fundamental differences among the terminals. Nonquantal release of ACh from motor nerve terminals arises at least in part from the movement of cytoplasmic ACh through the AChT located in the cytoplasmic membrane, and it is blocked by vesamicol. Possibly, the proteoglycan component of the AChT-VR produces long-term residence of the macromolecular complex in the cytoplasmic membrane through interaction with the synaptic matrix. The preponderance of evidence suggests that a significant fraction of what previously, heretofore, had been considered to be nonquantal release from the motor neuron actually is quantal release from the neuron at sites not detected electrophysiologically.(ABSTRACT TRUNCATED AT 400 WORDS)

Induction of choline acetyltransferase in the neuroblastoma x glioma cell line NG108-15

The mechanism of the induction of choline acetyltransferase activity in the hybrid cell line NG108-15 was studied. Induction by cyclic AMP analogs, forskolin, and prostaglandin E1 + theophylline was found to be rapid with an increase in choline acetyltransferase specific activity detectable within 8 hrs and maximal after 24 hrs. Immunoblot analysis was used to demonstrate that the increase in choline acetyltransferase specific activity induced by prostaglandin E1 + theophylline was due to an increase in enzyme protein. Cycloheximide effectively blocked the induction of choline acetyltransferase by prostaglandin E1 + theophylline. These results demonstrate that the induction of choline acetyltransferase activity involves the synthesis of new enzyme protein. Attempts to measure choline acetyltransferase turnover by blocking its synthesis with cycloheximide indicated that this enzyme is a relatively stable protein with a half-life of greater than 24 hrs.

Promoter elements of the rat choline acetyltransferase gene allowing nerve growth factor inducibility in transfected primary cultured cells

Choline acetyltransferase, the enzyme responsible for the synthesis of acetylcholine, provides a convenient index for cholinergic neurons. Using a previously identified rat cDNA clone, we have isolated several corresponding genomic clones and have characterized a 1,902-bp fragment that contains part of the first noncoding exon as well as promoter sequences. The promoter activity of this fragment was tested, taking advantage of the recently developed lipopolyamine-mediated DNA transfer method, which allows transfection of primary neurons. The 1,902-bp sequence drives the expression of the bacterial chloramphenicol acetyltransferase (CAT) reporter gene in a culture of dissociated cells prepared from the septal area of fetal (embryonic day 17) rats, a structure rich in cholinergic neurons. Moreover, addition of nerve growth factor to the culture increases CAT expression by approximately 56-fold, indicating that our DNA fragment contains sequences required for NGF induction. In addition, it contains consensus sequences for various transcription factors, including those of the basic helix-loop-helix family. Finally, experiments to characterize the transcription start site are presented.

Skeletal muscle proteins stimulate cholinergic differentiation of human neuroblastoma cells

Extracts of rat skeletal muscle contain substances that enhance the development of choline acetyltransferase (ChAT) in the cholinergic human neuroblastoma cell line LA-N-2. The ChAT enhancing activity in muscle extract was purified to homogeneity by preparative gel electrophoresis and reverse-phase HPLC. The active factor is biochemically and immunologically identical to ChAT development factor, (CDF), the skeletal muscle factor that enhances ChAT activity in enriched cultures of embryonic rat motoneurons and rescues motoneurons from naturally occurring cell death in vivo. CDF increases the specific ChAT activity of LA-N-2 cells fivefold after 6 days in culture, but does not affect their growth or metabolic activity. Basic fibroblast growth factor also increases ChAT activity in LA-N-2 cells and its effect is additive with that of CDF. In contrast, neither insulin-like growth factor-1, epidermal growth factor, nor nerve growth factor affected the ChAT activity of LA-N-2 cells. Our study demonstrates for the first time that CDF can directly affect the development of neuronal properties in a homogeneous population of cells, and that the effects of CDF are separate from those of other types of trophic factors.

Complexities and sequence similarities of mRNA populations of cholinergic (NS20-Y) and adrenergic (N1E-115) murine neuroblastoma cell lines

The clonal murine neuroblastoma cell lines NS20-Y and N1E-115 have been proposed as models for examining the commitment of neural crest cells to either the cholinergic or adrenergic phenotype, respectively. The validity of this model depends in part on the extent to which these two cell lines have diverged as a result of their transformed, rather than neuronal properties. In order to quantitate differences in gene expression between NS20-Y and N1E-115 cells, the mRNA complexity of each cell type was determined. An analysis of the kinetics of hybridization of NS20-Y cell mRNA with cDNA prepared from NS20-Y cell mRNA demonstrated the presence of approximately 11,700 mRNA species assuming an average length of 1900 nucleotides. A similar analysis using mRNA isolated from N1E-115 cells and cDNA prepared from N1E-115 cell mRNA demonstrated that the adrenergic cell line expressed approximately 11,600 mRNA species. The species of mRNA expressed by each cell line were resolved into high, intermediate, and low abundance populations. In order to determine whether mRNAs were expressed by the cholinergic, but not by the adrenergic cell line, NS20-Y cDNA was hybridized to an excess of N1E-115 cell mRNA. An analysis of the solution hybridization kinetics from this procedure demonstrated that the two cell lines do not differ significantly in the nucleotide complexity of their mRNA populations. The extensive similarity between the two mRNA populations suggests that only a small number of genes are expressed differentially between the two cell lines and supports their use as models for the differentiation of cholinergic and adrenergic neurons.

Enzymatic activities during differentiation of the human neuroblastoma cells, LA-N-1 and LA-N-2

The presence of 10(-5) M retinoic acid (RA) in the culture medium of LA-N-1, a catecholaminergic cell line, and LA-N-2, a cholinergic cell line, enhanced their morphological differentiation. Tyrosine hydroxylase (TH) activity of the LA-N-1 cells was increased in the RA-treated cells compared with control cultures at day 4 and remained elevated. Choline acetyltransferase (ChAT) activity in the LA-N-2 cells gradually increased until 8 days in vitro (DIV) both in the untreated control and the RA treated cultures. This activity in control and treated cells decreased gradually to a constant level of activity. The ChAT activity at 8 DIV of RA-treated LA-N-2 cells was increased 2.1-fold (P less than 0.001) as compared to the control cultures. This increase in ChAT activity was accompanied by a 73% decrease of acetylcholinesterase (AChE) activity in LA-N-2 cells by 8 DIV. AChE activity of LA-N-1 cells was unchanged during the time course of the experiment. Phospholipase-A2 (PL-A2) activity in RA-treated LA-N-2 cells was increased at day 4 as compared with the control cultures. There were no differences observed in phospholipase-D (PL-D), choline kinase and GPC-phosphodiesterases activities in RA-treated and -untreated LA-N-1 and LA-N-2 cells.

Regulation of viral and cellular genes in a human neuroblastoma cell line latently infected with herpes simplex virus type 2

A latent state of the herpes simplex virus type 2 genome was established in a human neuroblastoma cell line (SMS-KCNR) to initiate studies on the mechanism by which host cells interact and regulate latent viral genes. To establish viral latency, it was necessary to prevent virus replication by briefly exposing the infected cells to antiherpetic acycloguanosine (20 microM) and human interferon (120 U/ml). Subsequently however, these cells could be propagated without any antiherpetic agents and almost 60% of the cell population contained viral genome. While these cells did not produce any infectious virus, immunoblot analysis revealed two intracellular polypeptides with molecular weights of 87.5 kDa and 67 kDa, respectively, that interacted with hyperimmune anti-HSV2 rabbit serum. Two cellular enzymes, acetylcholinesterase and choline acetyltransferase, involved in metabolism of neurotransmitters were expressed at a higher level in the latently infected cells than in the mock-infected control cells. Infectious HSV-2 could be reactivated from these cells only after the cells had undergone massive morphological differentiation and maturation to flat cell types by extensive treatment with 20 micron bromodeoxyuridine.

Thyroid hormone actions on a cholinergic neuroblastoma cell line (S-20Y)

Thyroid hormone (T3) has a multiplicity of effects on the developing nervous system. We have investigated T3 action using a cholinergic neuroblastoma cell line (S-20Y) as a model. S-20Y contains a nuclear receptor for T3 with binding properties similar to those of other T3 target tissues. In addition, these cells can carry out 5'-deiodination, which is necessary to produce active thyroid hormone in vivo. The enzyme involved in this process appears to be a type I deiodinase, based on its reaction kinetics and its susceptibility to inhibition by propylthiouracil. S-20Y cells maintained in T3-depleted medium showed decreased choline acetyltransferase (ChAT) activity. ChAT activity was restored to the control level in a dose-dependent manner by T3 repletion. Neither cell density nor viability was influenced by the hypothyroid state. The presence of a T3 receptor and the enzyme activity for T3 production, together with an effect of T3 on ChAT activity, demonstrate that S-20Y cells are a target for T3 action and suggest that these cells represent an excellent model system for studies of T3 effects on nervous tissues.

Altered cellular functions in a PC-12 cell clone chronically infected with retrovirus

We characterized retrovirus-induced changes in PC-12 cell function and neuronal differentiation. PC-12 cells were infected with a neurotropic retrovirus (temperature-sensitive Moloney murine leukemia virus, mutant BA-1). We isolated a cell clone from this infected culture that displayed altered response to nerve growth factor; increased choline acetyltransferase activity; and decreased basal and nerve growth factor-stimulated acetylcholinesterase activity. In addition, Kirsten murine sarcoma virus infection of and subsequent expression of the v-ras oncogene in PC-12 cells induced neurite extension, enhanced choline acetyltransferase activity, and limited the growth potential of the infected cells.